The invention relates to a rotary drive with a speed changing means for a tool holding device as is for instance described in the patent publication WO 99/127000. Modern machining centers are frequently designed for machining by turning and also milling. The tool holding means is thus designed for milling and turning tools, for which purpose a common tool changing device is often provided. During milling the tool is subjected high torques at a relatively low speed of rotation whereas during machining by turning at low torques speeds of rotation are high. Accordingly the rotary drive for the tool holding device requires a speed changing means, which does justice to the different torques required.
One object of the invention is to provide an improvement and simultaneously a simplification of the known rotary drive having a means for changing the speed of rotation to meet said requirements.
In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention a rotary drive for a tool holding device meets this requirement because it possesses an output drive shaft bearing the tool holding device and which is able to be moved by means of a setting drive into two different axial positions, the output drive shaft being coupled in the first axial position with a power driven first drive gear wheel and in the second axial position with a concentric tubular shaft, which is driven by the intermediary of a worm drive from a second power driven drive gear wheel.
The rotary drive of the invention is, unlike the known rotary drive, completely free of collets, brake jaws and brake disks, which at the torques involved are subjected to undesired wear. The changing of speed takes place in a simple manner using a single, simple setting drive by axial movement of the output drive shaft between two coupling positions. The power drive can in the case of this rotary drive be designed in a simplified manner. Furthermore, the rotary bearings for the different components are simplified in the rotary drive of the invention.
The claims define features representing advantageous further developments and improvements in the rotary drive.
The two drive gear wheels are preferably able to be driven using a gear wheel or toothed belt drive from an electric motor so that there is an economic, simpler and readily assembled power drive. For the coupling between the output drive shaft and the first drive gear wheel on the one hand and the concentric tubular shaft on the other hand it is best for two coupling means of the Hirth type to be provided.
Owing to the exclusive use of toothed couplings a reliable and low-wear coupling means is realized, by which heavy torques may be transmitted.
In keeping with an advantageous form of this coupling the output drive possesses two radial tooth rings, of which the first one in the first axial position of the output drive shaft meshes with a radial gear ring of the first drive gear wheel and the second meshes in the second axial position of the output drive shaft with a radial tooth ring on the concentric tubular shaft, the teeth of the two radial tooth rings of the output drive shaft preferably being oppositely directed. It is therefore possible to switch over between the first coupling and the other coupling simply by a small shift of the output drive shaft.
In keeping with a preferred form of the setting drive same possesses a second concentric tubular shaft, which is rotatably mounted on the output drive shaft and is axially coupled with same, a setting member being provided for axially shifting the second concentric tubular shaft. This setting member is preferably arranged between the second tubular shaft and the axially fixed first tubular shaft and is more particularly in the form of a fluid power setting cylinder, which preferably is simply constituted by an annular groove machined therein and an annular element fitting into the groove. The output drive shaft can consequently be axially shifted by the second concentric tubular shaft without such second axial tubular shaft having to rotate with it.
Using a coupling means actuated by the setting drive for decoupling the second drive gear wheel from the first concentric tubular shaft in the axial position of the output drive shaft it is possible to ensure that such second drive gear wheel is able to continuously rotate therewith, and is thus constantly drivingly connected with the drive motor despite the fact that the worm drive and accordingly the rotary movement of the first concentric tubular shaft is able to be decoupled, when such movements are not required. This means that wear of the respective components is reduced.
In accordance with an advantageous design of the coupling means the second concentric tubular shaft possesses an entraining dog for causing corresponding axial displacement of a coupling gear wheel having radial teeth, which is arranged on a drive shaft of the worm drive with which it is locked in rotation while being able to be slid axially and is furthermore able to be coupled with a radial gear ring on the second drive gear wheel. Here as well there is again an absence of any friction coupling.
In a convenient development of the invention the worm drive possesses an annular worm wheel keyed on the first concentric tubular shaft and furthermore a worm drivingly connected with the same, such worm being able to be driven by the second drive gear wheel, more especially by way of an angle drive.
It is an advantage for the first concentric tubular shaft to be rotatably mounted as an outer tubular shaft in a housing of the rotary drive, bearing means preferably being provided to take up axial forces occurring during machining.